The present invention relates to molecular sieves produced from carbonacious materials, which have functions of separating mixtures of molecules having different molecular sizes into groups of molecules based on the differences in the selective adsorbability of the molecules.
A variety of processes for producing carbon molecular sieves have been reported since Emmett obtained a carbon molecular sieve by carbonizing polyvinylidene chloride resin (P. H. Emmett: Chme. Rev. 43, page 69). For example, Japanese Patent Publication No. 37036/1974 discloses a process which comprises polymerizing or condensing prepolymer of phenol or furan resin adsorbed on the surface of activated carbon, and then carbonizing the resin thus formed on the surface by heating at 400.degree. to 1000.degree. C. Japanese Patent Publication No. 18675/1977 discloses a process for producing a molecular sieve, which comprises holding a coke having not more than 5% of volatile matters in an inert gas atmosphere at 600.degree. to 900.degree. C., adding a gaseous hydrocarbon that discharges carbon upon thermal degradation, and permitting the carbon that forms by the decomposition to deposit in micropores to decrease the pore diameters. The essential element of this process is to blow a gaseous hydrocarbon into the furnace and to thermally decompose the hydrocarbon at high temperature. Japanese Patent Publication No. 8004/1986 discloses a process which comprises carbonizing pelletized coal, then, after washing the obtained carbon pellets with a mineral acid to remove alkali metal salts, impregnate the granules with 1-3% of coal-tar pitch or coal tar, and heat treating the granules at 950.degree. to 1000.degree. C., followed by cooling in an inert gas atmosphere. Further Japanese Patent Application Laid-open No. 176908/1987 discloses a process for producing a molecular sieve having still higher performance, which comprises using, instead of the coal-tar pitch or coal tar in the above-mentioned process, a fraction of creosote having boiling points of 140.degree. to 260.degree. C., dimethylnaphthalene or xylenol.
Kitagawa (Nenryo Kyokai-Shi, 60 No. 654, 859-864 (1982) describes a process for producing a high-performance molecular sieve which comprises adding 4 to 5% of sulfite pulp waste liquor and coal-tar pitch to Yallourne char powders, pelletizing the mixture and heating the pellets at a constant temperature elevating rate to 600.degree. to 700.degree. C., followed by heat treatment for 1 hour.